1. Field of the Invention
The present invention relates to a storage system including computers used by users and a storage device shared by these computers. In particular, the present invention relates to access control to a logical unit of the storage device shared by the computers.
2. Description of the Related Art
A storage system includes several computers which can be used by any user and a storage device shared by the computers. In the storage system, working environment information of the computer for each user is stored in a logical unit (LU) in the storage device which is located at, for example, a data center. In other words, each user owns a LU in the storage device. In such a storage system, a user does not own any computer.
These computers and the storage device are connected via a network, for example, a Storage Area Network (SAN), using a fiber channel technique. The user can use own working environment information through any computer connected to the storage device via the SAN.
None of the computers connected via the SAN have a hard disk. The computers can be used by any user. In brief, the computers and users do not have the relationship of one-to-one correspondence, and instead have a relationship of N-to-M. The number of computers is denoted by “N” and the number of users is denoted by “m”.
The foregoing storage system has the following two advantages. First, the user is not required to carry around a computer, and can use a computer provided at each branch office given as per the infrastructure. Second, the user can arbitrarily select and use any of non-used computers; therefore, the computer availability is enhanced.
For example, large enterprises have many branch offices all over the world. In this case, working environment information of all employees are stored in the storage device located at the company data center. Here, the working environment information includes an operating system, application software, those configurations and data which are used by the employee.
Any computer provided at any of the branch offices can be connected to any user's working environment information. By doing so, any user can use any computer as if it were own computer. For example, even if the employee goes to another branch office on business, the employee can access own working environment information.
However, the foregoing storage system has the following problem. Namely, the computers and the users have the relationship of N-to-M correspondence; for this reason, a mutual exclusion problem arises among computers and among users.
The computer used for the foregoing storage system includes no hard disk. For this reason, when the user turns off the computer to end the use of the computer, no data remains on the computer. Thus, even if several users sequentially use the same computer, the following user is in no way affected by how the previous user uses the computer; therefore, there is no mutual exclusion problem.
On the other hand, the operating system was traditionally stored in a hard disk of each computer; for this reason, it is not designed to work on multiple computers simultaneously. For example, in the case that a user forgets to turn off the power of a computer connecting own working environment information, and subsequently connects to own working environment information from another computer, the operating system malfunctions. As a result, there is a possibility that data is destroyed. In other words, if several computers simultaneously access the same working environment information, a mutual exclusion problem arises.
In order to solve the foregoing problem, the following technique is disclosed (see Jpn. Pat. Appln. KOKAI Publication No. 2001-75853). According to the technique, a table showing a relationship between computers and LUs storing working environment information of users is stored in the storage device. Then, an accessing LU is mapped in the table depending on the connected computer. The technique can solve the foregoing mutual exclusion problem because the computer accesses the working environment information in only correspondence of the intended computer and the working environment information.
According to the foregoing technique, only the computer corresponding to the LU storing the working environment information can access the working environment information. Therefore, the mutual exclusion problem is solved.
However, when the correspondence of the computer and the working environment information changes, namely, the user changes the using computer, storage device configuration of correspondence between computers and LUs must be changed every time.
Thus, a change of the correspondence of the computer and the working environment information is accurately grasped to always reflect it in the storage device.
However, this is difficult in a storage system in which many users exist, and the correspondence of users and computers changes variously in accordance with requests from users.